Cut the ham into dice. Season the flour with a little salt and pepper on a plate. Cut the turkey into small chunks and coat with the seasoned flour.
Melt the butter in a flameproof casserole and fry the turkey for 5 minutes until golden on all sides. Add the onions and celery to the casserole and fry for 4–5 minutes until softened. Tip in any remaining flour left on the plate. Blend in the stock, add the thyme and chilli powder and bring to a simmer, stirring.
Cover the casserole and cook in a preheated oven, 180°C (350°F), Gas Mark 4, for 45 minutes.
Stir the sweet potatoes and ham into the casserole and return to the oven for a further 30 minutes. Stir in the cranberries and crème fraîche and season to taste with salt and pepper. Return to the oven for a final 15 minutes before serving.